This invention relates to methods and apparatus for manufacturing stators, more particularly, this invention is directed toward producing stators having undulating or wave wound coils which are formed and inserted into the stator lamination stack.
Armatures and stators for dynamo-electric machines have a broad range of applications. Common examples of the wide use of dynamo-electric machines include: automobile alternators, electric drills, generators, etc. Due to the widespread use of these machines, there is an ever increasing demand for the armatures and stators from which they are typically produced.
In order to meet these demands, machine manufacturers have continued to increase the use of automation. In a typical forming and insertion automated stator manufacturing operation, stators are fed down an assembly line on pallets from workstation to workstation, sequentially, where incremental manufacturing of the stator occurs. These workstations may include such tasks as winding the stator coils (a typical stator has multiple wound coils), insertion of the wound coils within the stator lamination stack, and forming of the coils to accommodate further processing.
Unlike armature windings which are generally wound directly on the armature, stator windings may be produced external to the stator and then inserted into slots in the stator stack. Examples of machines which produce stator coils are described in U.S. Pat. Nos. 4,512,376 and 4,580,606. These patents describe apparatus for forming undulatory (or waveform) stator coils consisting of multi-lobed turns, and for placing the formed coils on an inserter tool. The formed coils are then inserted into the stator stack in a further step.
A single workstation may individually form and insert all of the coils for a stator (typically, three coils are required for a three-phase stator), although this technique tends to be highly inefficient due to the waiting time required while each coil is formed. Depending on the "fill density" of the stator, (a combination of the number of wires per slot and the number of slots per lamination stack) it may also be possible to simultaneously insert multiple wound phases into a single stack using a special insertion tool. Alternatively, each workstation of the stator assembly line may completely perform the forming and insertion of a single coil (corresponding to one phase of the multi-phase stator) and there may be additional workstations for each additional phase of the stator to increase overall efficiency of the assembly line.
Often, a stator assembly line incorporates temporary storage locations to account for a loss of synchronization between workstations. For example, occasionally a downstream station requires more time to complete its task than the previous station; therefore, a slight buildup of pallets in the storage location between the stations occurs. Another common problem which leads to pallet build-up involves temporary shutdowns of a machine for regular maintenance--for example, to refill an empty wirefeed.
To avoid a permanent condition of pallet build-up, the production rates of the various workstations may require frequent calibration, which may cause the higher efficiency machines to be adjusted at a production rate of the lowest efficiency machine in the line--an obviously undesirable condition. Unfortunately, even temporary build-up results in a loss of production efficiency because the upstream station must eventually slow down to permit the downstream station to recover. This problem becomes even more severe when the production rates on multiple stations within the stator assembly line become unequal.
An even greater problem occurs when any single production station in the line must be shut down. As described above, a temporary shutdown for regular maintenance, which may occur on a daily basis, may be completed without having to shut down the entire line, but the storage areas will become significantly backed up. On the other hand, a permanent shutdown of a station essentially shuts down the entire line, causing significant losses in productivity, thereby increasing overhead costs. Therefore, maintenance is often scheduled on multiple machines within an assembly line leading to higher operational costs (e.g., wirefeeds may be replaced before they are empty to coordinate maintenance shutdowns). obviously, it would be preferable to avoid the severe impacts of having to shut down the entire assembly line due to a single machine. It would be even more advantageous if the assembly line were designed such that machines could be temporarily removed from the line without having to shut down the entire line.
An additional deficiency of previously known stator production lines is related to adjustments in operational capacity. In traditional stator production lines, where components move serially down a line from dedicated machine to dedicated machine, the ability to increase production capacity on the line is limited to the highest production rate of any single machine. Likewise, any reduction is capacity is typically performed by simply lowering the overall production rate, thereby causing production equipment to be used inefficiently.
In view of the foregoing, it would be desireable to be able to provide improved methods and apparatus for manufacturing stators having wound coils.
It would also be desireable to provide improved methods and apparatus for manufacturing stators in which wave wound coils are preformed and inserted within the stator stack.
It would further be desireable to provide a stator manufacturing system having multiple workstations, each workstation being able to preform and insert the wave wound coils in the stator stack.
It would more particularly be desireable to provide a stator manufacturing system which continues to be able operate after a workstation has been shut down.
It would additionally be desireable to provide a stator manufacturing system in which production capacity can easily be adjusted.